Galaxies and Cosmology 5 points, vt-2007 Teacher: Göran Östlin Lecture 3

Practical info Language? English or Swedish? Registration Who am I, who are you? Assistants: Jens, Teresa and Michael Course book: Jones & Lambourne + extra material (handed out + www). The book is up to date and comprehensive, but a bit ”easy” Course www-page continously updated Lectures L1-L12 Exercise sessions Hand in exercises -> bonus points (max 3x2) on exam 2 Laboratory exercises (mandatory): Get 1 bonus point on the exam if OK before (hand in latest 5/6). Tenta/Exam, max 30 points G (18 points) or VG (24)

Hydrostatic equilibrium: Sound cross time Free fall time Collapse if Star formation

Stars are born in dusty molecular clouds Dust allows the gas to cool Jeans mass for typical molecular clouds solar masses Contraction leads to decreasing M jeans and fragmentation Star formation is collective => populations

R136 cluster of young stars

IMF: initial mass function Young massive stars in R136 (Massey & Hunter)

IMF: Salpeter (1955): Massey & Hunter confirmedSalpeter Slope for young masssive stars

Unveiling the IMF in the solar neighbourhood is more complex due to the presence of many stellar generations

IMF of the Pleiades young star cluster Simple = Single Stellar Population (SSP)

Herzsprung-Russel / Colour-Magnitude Diagram (HR diagram / CMD) Not SSP

Nearest stars Brightest stars

Iso-chrones Positions of stars of given age = SSP RGB more sensitive to metallicity than age Metal-rich Metal-poor

observed CMDs for two ”simple/single stellar populations”

Globular cluster CMDs

Parallax & parsecs For example, a star that has a parallax of say 1 arc second will be at a distance of:

The Milky Way Galaxy a.k.a. the Galaxy (galaxias kyklos) NB this is a painting, not a photograph

Milky Way Galaxy Appearance, size, morphology –Disk, bulge, halo Constituents: –Stars of various populations –Gas (cold, warm, hot) and dust = ISM –Dark matter Dynamics Evolution and recycling Galactic centre

The local group, a photo montage

Artist’s impresseion The Milky Way Galaxy Galaxy = MW galaxy = others

Milky way look alike

NGC 891 MW (COBE)

Equatorial vs Galactic coordinates

Extent of optical emission (starlight) vs 21cm (neutral gas) In Milky Way and other spiral galaxies 21 cm spin flip transition of neutral Hydrogen (H I ) (see box 1.3, page 30)

Nearest stars Brightest stars Nearest stars dominated by low luminosity brighest stars dominated by high because these are most commonlumionsity as we can see them far away

Pleiades young star cluster Horsehead nebula in Orion Pop I = young Stars in the disk

Globular cluster (population II) on the order of a million stars, gravitationally bound

X-ray binaries in globular cluster ”47 Tuc”

Colour distribution of halo and disk stars - Age vs Metallicity

Metal-rich Globular Clusters (near the plane) Metal-poor Globular Clusters (in the halo)

Vertical distribution of stars Disks have exponential light distribution: I = surface brightness, h = scale length (height) Thin (h z = 300 pc) vs Thick (h z = 1 kpc) Disk Thick disk older, hence no A-stars

Disks have exponential light distribution: I = surface brightness, intensity (flux per angular area) h = scale length (height) Surface photometry NB surface brightness independent of distance - Flux per angular area - Luminosity per metric area

Radial distribution of neutral atomic (H I ) and molecular (H 2 ) gas in the Milky Way Galaxy H 2 has no ’dipole moment’ and therefore no suitably observable transitions at typical ISM cloud temperatures, but the CO molecule can be used as tracer (see Box 1.4 on page 33 in JL)

PropertyPopulation IIntermediatePopulation II OrbitsCircularElongatedVery elliptical Shapespiral armsdiskspherical/halo Thickness(pc) Metals (%) or less Mass (M sun )2x10 9 5x x10 10 Age (yr) Typical objectsOpen clusters, Sun Globular clusters HII regions, RR Lyrae stars Stellar populations in MW Population III ? Zero metallicity

Chemical composition of star clusters in MW

High lattitude neutral hydrogen